Cavitating throttling valve

ABSTRACT

To provide a definable and repeatable transition between noncavitating and cavitating flow in a variable area venturi valve, a flow straightener is included upstream of a valve seat and metering plug assembly. Cavitating venturi valves meter the flow of fluid therethrough between the metering plug and the valve seat. The metering plug and the valve seat have a geometry that in cross section resembles a venturi. The valve straightener resembles a plurality of parallel passageways having a length to width ratio to collimate a flow of fluid passing therethrough.

United States Patent Usry [4 1 Man-7,1972

[72] Inventor:

[54] CAVITATING THROTTLING VALVE Joe D. Usry, Arlington, Tex.

[73] Assignee: LTV Electmsystems, 1ne., Greenville, Tex. 221 Filed: June23, 1970 [21] Appl. No.: 49,048

[52] US. Cl ..25l/l22 [51] Int. Cl ..Fl6lt 47/00 [58] Field of Search..25l/48, 121,122, 205; 138/45, 138/46 [56] References Cited UNITEDSTATES PATENTS 1,921,761 8/1933 Leins ..251/l22 1,980,752 11/1934Eskilson et a1. ..25l/D1G. 4

3,013,767 12/1961 Del-laven ..251/122 3,317,184 5/1967 Usry ..25l/l22Primary Examinerl-lenry T. Klinksiek Att0rney-Richards, Harris & Hubbard[57] ABSTRACT To provide a definable and repeatable transition betweennoncavitating and cavitating flow in a variable area venturi valve, aflow straightener is included upstream of a valve seat and metering plugassembly. Cavitating venturi valves meter the flow of fluid therethroughbetween the metering plug and the valve seat. The metering plug and thevalve seat have a geometry that in cross section resembles a venturi.The valve straightener resembles a plurality of parallel passagewayshaving a length to width ratio to collimate a flow of fluid passingtherethrough.

6 Claims, 5 Drawing Figures PATENTEDMAR H972 I 3.647.176

' SHEEY1UF3 1 26 l J j FIG. I

INVENTORI JOE I D. USRY M4, m uw ATTORNEYS PATENTEDMAR 71972 3,647. 176

sum 2 [1F 3 X X X X PS 2 3 5 I I I I I INVENTORI FIG. 3 JOE 0. USRYATTORNEYS PATENTEUMAR 7 I972 3.647. 176

SHEET 3 OF 3 I Xmox I NON-CAVITATING Li CAWTATING I 40 x O Qm x FIG. 6

iNVENTORI JOE D. USRY ATTORNEYS CAVITATING TIIROTTLING VALVE Thisinvention relates to a cavitating venturi valve, and more particularlyto a cavitating venturi valve including a collimator for producing lessturbulent flow through the metering orifice.

l-Ieretofore, the cavitating venturi has been used successfully as aflow control valve because it exhibits a choked" flow behavior fornoncompressible fluids similar to that of the supersonic nozzle forcompressible fluids. Both effects show flow rate saturation (constantflow) when the back pressure on the metering orifice is maintained abovea certain level. This phenomenon that produces a constant flow withvariations in back pressure has been found to be advantageous inapplications where it is necessary to decouple (isolate) thefluid-consuming load from the supply system. With the cavitatingventuri, variations in the pressure drop of the load will not affect thefluid mass flow into the load.

In addition to fixed flow cavitating venturi controls, the cavitatingflow phenomenon has also been incorporated into variable area meteringvalves. Such a valve meters between a metering plug and a valve seatassembly having a geometry that in cross section resembles a venturi.These valves have been found to be particularly useful for rocketengines on space exploration vehicles. In rocket engine applications,and in most applications of variable area venturi metering valves, spaceis at a premium and the flow path tends to be somewhat tortuous. Thisresults in turbulent flow through the metering section of the valve.Such turbulent flow reduces the valve efficiency, but, more importantly,prevents accurate knowledge of at what flow rate a particular valve willoperate in the cavitating mode.

An object of this invention is to provide a venturi valve havingpredictable choked flow behavior. Another object of this invention is toprovide a venturi valve having substantially nonturbulent flow throughthe metering area. Still another ob ject of this invention is to providea venturi valve having increased pressure efiiciencies. A still furtherobject of this invention is to provide a venturi valve having a flowstraightener upstream of the metering area.

In accordance with the objects of this invention, a cavitating venturivalve includes a diffuser in the plenum chamber of a housing; thehousing having an inlet passage and an outlet passage. The diffuser islocated between the inlet passage and theoutlet passage and includes avalve seat. A metering plug is adjustably mounted in the plenum chamberto form a variable metering area with the valve seat. This plug isshaped to form a cavitating flow pattern through the diffuser andcontrols the rate of flow by a change in spacing between the meteringplug and the valve seat. To provide predictable cavitating flow behaviorthrough the valve, a flow collimator (flow straigtener) is positioned inthe plenum chamber upstream of the diffuser. The collimator develops aless turbulent flow pattern for a fluid passing through the diffuser.

In accordance with another aspect of this invention, a cavitatingventuri valve includes a housing having an inlet passage and an outletpassage communicating with a plenum chamber. A cylindrical-shapeddiffuser with a substantially straight wall bore is mounted in theplenum chamber between the inlet passage and the outlet passage. Thisdiffuser includes a valve seat toward the upstream end. Forming avariable metering area with the valve seat is a metering plug having ageometry that will form a cavitating flow pattern through the straightwall bore diffuser. By adjusting the spacing between the metering plugand the valve seat, the rate of flow through the valve is controlled. Aflow collimator, in the form of a plu' rality of parallel passageways,is positioned in the plenum chamber upstream of the diffuser tocollimate the flow of fluid from the inlet passage through the diffuser.

A more complete understanding of the invention and its advantages willbe apparent from the specifications and claims and from the accompanyingdrawings illustrative of the invention.

Referring to the drawings:

FIG. 1 is a sectional view of a cavitating venturi valve including aflow collimator (straightener) in accordance with the present invention;

FIG. 2 is a cross section of FIG. 1 taken along the line 2-2;

FIG. 3 is a plot of the pressure drop across a cavitating variable areaventuri valve versus the flow rate through the valve for differentmetering plug positions;

FIG. 4 is a plot of the metering plug position of a variable areaventuri valve versus flow rate through the valve;

FIG. 5 is a cross section of a metering plug and diffuser assemblyillustrating an alternate embodiment of a flow straightener; and

FIG. 6 is a cross section of the embodiment of FIG. 5 illustrating theposition of the metering plug and flow straightener for maximum valveflow.

Referring to FIGS. 1 and 2, there is shown a variable area venturimetering valve wherein the inlet and outlet flow directions are at anangle with respect to the metering flow direction. In the valve shown, ahousing 10 includes a plenum chamber 12 having an inlet passage 14communicating therewith on one side and an outlet passage 16communicating therewith on the opposite side. Within the chamber 12 is adiffuser 18 having a substantially straight bore cylinder section 20forming a conduit between the inlet passage side and the outlet passageside of the plenum chamber.

A metering plug 22 at the end of a positioning rod 24 is slidablypositioned within the chamber 12 and moves coaxial with the straightbore cylinder section 20 of the diffuser 18. The metering plug 22 ispositioned by means of a servomotor mechanism (not shown) coupled to thepositioning rod 24. A spring 26 biases the metering plug 22 into contactwith a valve seat 28 formed at the upstream end of the diffuser 18. Asillustrated, the metering plug 22 closes off the fluid flow path betweenthe inlet passage 14 and the outlet passage 16.

In the embodiment shown, the metering plug 22 has a generally conicalconfiguration tapering toward the direction of flow. With the straightbore cylinder diffuser l8 and theconical-shaped metering plug 22, thereresults a venturi geometry that is capable of producing a cavitatingflow pattern.

Fluid entering the plenum chamber 12 through the inlet passage 14 willflow in a turbulent pattern. This turbulent flow adversely affects thecavitating venturi valving of the metering plug 22 and the diffuser 18,as will be explained in FIG. 3. To produce a less turbulent patternthrough the diffuser 18, a flow collimator 30 is mounted in the plenumchamber 12 upstream of the diffuser 18. As shown in FIG. 2, thecollimator 30 includes an outer ring 32 with a plurality of inwardlyextending radial fins 34 secured thereto. The fins 34 form a pluralityof parallel passageways between the upstream section of v the plenumchamber 12 and the diffuser 18. The fins 34 are evenly distributedcircumferentially and form passageways having a sufficient total flowcapacity to provide the required maximum flow of liquid through thediffuser l8. Dimensionally, the fins 34 have a ratio of length in thedirection of flow to width in the direction transverse to flowsufficient to collimate a stream of fluid as it passes from the inletpassage 14 to the outlet passage 16. The length in the fins in thedirection of flow is typically on the order of two or three times thedistance between adjacent fins. An additional design criterion is thatthe fins have a width in a direction transverse to flow such that theratio of the diameter of the plenum chamber 12 to the fin width is onthe order of 4 to I.

As an aid in understanding the operation of a cavitating venturi valve,an explanation of the phenomenon of cavitation is presented. When anoncompres sible fluid undergoes a contraction and an expansion througha venturi-type section, the pressure is reduced at the minimumcontraction section as the fluid velocity increases according to'Bemoullis equation and the equation of continuity as follows:

where P V and A, are the pressure, volume and area of the upstreamsection of the venturi, P V and A, are the pressure, volume and area ofthe venturi throat, and P V and A are the pressure, volume and area ofthe downstream section of a venturi. The above relationship, however,-isno longer true when the minimum pressure reaches the vapor pressure(P,., new, P,=P,. When the vapor pressure is reached, the pressure atthe venturi can be reduced no further and the flow remains constant.After passing through the venturi throat the pressure is regainedthrough the diffuser 18 to the downstream pressure P The pressure dropacross the illustrated valve versus flow rate varies with the loadapplication. The valve pressure drop necessary to drop the total supplypressure at the inlet passage 14 to that required by a load connected tothe outlet passage 16 is obtained by subtracting the required loadpressure drop from the supply pressure. The valve pressure drop turnsout to be a function of the load requirements. For a cavitating valve,the pressure schedule (valve pressure drop) should be such that thevalve always operates in a region of cavitation. The maximum pressurerecovery permissible for a cavitating valve is a ratio of the maximumback pressure to the supply pressure when the valve is at the point ofincipient cavitation.

Referring to FIG. 3, there is shown pressure drop across a typical valveversus the flow rate through the valve with varying back pressure, thatis, load pressure. Starting from a zero pressure drop across the valve,the flow rate proceeds along a square law curve until the point ofincipient cavitation, then the flow rate is constant even though thepressure drop across the valve changes. The family of curves of FIG. 3shows the characteristics of a valve for different positions (x x x ofthe metering plug 22.

With a specified pressure drop versus flow rate schedule, the flow rateversus plug stroke can be plotted as shown in FIG. 4. It will be notedin FIG. 3, that the shaped plug has linear flow versus strokecharacteristics as long as the pressure schedule, line 40, crosses theflow versus pressure drop family of curves in the cavitation region, butchanges to a lower flowstroke gain when the pressure schedule, line 42,crosses the square law curves. Thus, the pressure schedule of a valveshould be such that operation is always in the cavitation mode.

Without the flow straightener 30, the transition from the noncavitatingmode of operation to the cavitating mode is unstable. That is, the comerat which the flow changes from the noncavitating to the cavitatingpattern varies with flow rate and is not predictable, as illustrated bythe dotted lines of FIG. 3 for each metering plug position. The flowstraightener isolates the flow at the valve seat 28 from upstreamturbulence and the change into the cavitating mode becomes predictableand repeatable.

To cause the valve to cavitate, the passage downstream of the meteringorifice, i.e., the valve seat 28, must be an efficient diffuser. One ofthe most efficient diffusers for a variable metering area valve, asillustrated in FIG. 1, is a straight bore cylinder. The diameter of thevalve seat 28, and thus the diameter of the diffuser channel 20, isdetermined by the stroke of the metering plug 22 and the taper of theconical section of the plug. It has been shown, that efiicient anglesfor the cone-shaped plug are between 4 and In a model of a cavitatingventuri valve in accordance with the present invention, the valve seat28 was configured as having a0.5-inch short radius, i.e., short of afull radius by about 20. The angles of the cone of the metering plug 22varied from 4 to 10 to obtain the correct linear flow versus plugdisplacement relationship. A plug stroke of 0.25 inches was used with aseat diameter of 0.434 inches. The diffuser 18 had a substantiallystraight bore configuration.

An alternate embodiment of the venturi valve is illustrated in FIGS. 5and 6, only the metering assembly is illustrated.

Referring to FIG. 5, a diffuser 36 having a substantially straight wallcylindrical bore 38 and a flow-straightening cylinder 39 is mountedbetween the inlet passage side and the outlet passage side of a plenumchamber. A metering ghg 40, having a generally conical section taperlnginto a s a 42,

forms a metering valve with the diffuser 36. To change the rate of flowthrough the valve, the spacing between the plug 40 and a valve seat 44of the 36 is varied. In FIG. 5, the metering plug 40 is shown at about10 percent flow rate position.

Mounted to the top section of the plug 40 is a flow straightener 48consisting of a circular collar with a plurality of circumferentiallyspaced radially outwardly extending fins. These fins from a plurality ofparallel passageways between the turbulent upstream flow and thediffuser 36. With the embodiment of FIGS. 5 and 6, the flow straightener48 moves with the metering plug 40 within the cylinder 39. In FIG. 6,the metering plug is shown in the 100 percent flow position with theflow straightener 48 displaced from the difl'user 36.

While several embodiments of the invention, together with modificationsthereof, have been described in detail herein and shown in theaccompanying drawings, it'will be evident that various furthermodifications are possible without departing from the scope of theinvention.

What is claimed is:

1. In a cavitating venturi valve comprising:

a housing having an inlet passage and an outlet passage communicatingwith a plenum chamber,

a cylindrically shaped diffuser with substantially straight wallsections in said chamber between the inlet passage and the outletpassage and including a valve seat toward the upstream end,

a metering plug in said chamber having a tapered first section formating with the valve seat to shut off a flow from the inlet passage tothe outlet passage and a cone-shaped second section contiguous with thefirst section converging from the first section in the direction offluid flow to form a venturi with said cylindrical-shaped diffuser toproduce a cavitating flow pattern through said diffuser for controllingthe rate of flow through said valve by a change in the spacing betweensaid plug and the valve seat, and

a flow collimator in said chamber between the inlet passage and saiddiffuser to develop a nonturbulent flow for a fluid passing through saiddiffuser.

2. A cavitating venturi valve as set forth in claim 1 wherein saidhousing has the inlet passage communicating with the plenum chamberat anangle less than to the flow through said diffuser.

3. A cavitating venturi valve as set forth in claim 2 wherein saidhousing has the outlet passage communicating with the plenum chamber atan angle greater than 90 to the flow through said diffuser.

4. A cavitating venturi valve as set forth in claim 3 wherein said flowcollimator includes a plurality of parallel passageways in said chamberhaving a ratio of length, in the direction of fluid flow, to width, in adirection transverse to fluid flow, sufficient to collimate the flow offluid from the inlet passage through said cylinder.

5. A cavitating venturi valve as set forth in claim 3 wherein said flowcollimator includes a cylindrical collar having a plurality ofcircumferentially spaced fins extending radially attached thereto tocollimate a flow of fluid from the inlet passage through said straightbore cylinder.

6. A cavitating venturi throttling valve as set forth in claim 3 whereinsaid flow collimator includes a collar mounted to said metering plug,said collar having a plurality of circumferentially spaced finsextending radially therefrom and attached thereto to collimate a flow offluid from the inlet passage through said straight bore cylinder.

1. In a cavitating venturi valve comprising: a housing having an inletpassage and an outlet passage communicating with a plenum chamber, acylindrically shaped diffuser with substantially straight wall sectionsin said chamber between the inlet passage and the outlet passage andincluding a valve seat toward the upstream end, a metering plug in saidchamber having a tapered first section for mating with the valve seat toshut off a flow from the inlet passage to the outlet passage and acone-shaped second section contiguous with the first section convergingfrom the first section in the direction of fluid flow to form a veNturiwith said cylindrical-shaped diffuser to produce a cavitating flowpattern through said diffuser for controlling the rate of flow throughsaid valve by a change in the spacing between said plug and the valveseat, and a flow collimator in said chamber between the inlet passageand said diffuser to develop a nonturbulent flow for a fluid passingthrough said diffuser.
 2. A cavitating venturi valve as set forth inclaim 1 wherein said housing has the inlet passage communicating withthe plenum chamber at an angle less than 90* to the flow through saiddiffuser.
 3. A cavitating venturi valve as set forth in claim 2 whereinsaid housing has the outlet passage communicating with the plenumchamber at an angle greater than 90* to the flow through said diffuser.4. A cavitating venturi valve as set forth in claim 3 wherein said flowcollimator includes a plurality of parallel passageways in said chamberhaving a ratio of length, in the direction of fluid flow, to width, in adirection transverse to fluid flow, sufficient to collimate the flow offluid from the inlet passage through said cylinder.
 5. A cavitatingventuri valve as set forth in claim 3 wherein said flow collimatorincludes a cylindrical collar having a plurality of circumferentiallyspaced fins extending radially attached thereto to collimate a flow offluid from the inlet passage through said straight bore cylinder.
 6. Acavitating venturi throttling valve as set forth in claim 3 wherein saidflow collimator includes a collar mounted to said metering plug, saidcollar having a plurality of circumferentially spaced fins extendingradially therefrom and attached thereto to collimate a flow of fluidfrom the inlet passage through said straight bore cylinder.